A large number of heat exchanger tubes (heat transfer tubes) are provided to a shell (body) of a heat exchanger. A long-term operation of a heat exchanger may cause corrosion thinning, corrosion cracks, hydrogen embrittlement cracks, or the like in a body or a heat transfer tube of the heat exchanger. Therefore, the heat transfer tube of the heat exchanger is subjected to periodic inspection, in which a thickness thereof is measured. When a portion of the heat transfer tube where the thickness of the tube has been too reduced, due to corrosion, to potentially cause breakage such as holes by the next inspection, a repair is performed.
For example, a frequency of the inspection is set as follows: (A) the periodic inspection for the entire plant is performed every two years, and the inspection continues for about two months; (B) a small-scale inspection is performed one year after the periodic inspection, and the inspection continues for about two weeks; (C) in addition, the plant may be stopped irregularly for about two days to one week.
Generally, when there is a possibility of occurrence of breakage of the heat transfer tube due to thinning thereof by the next inspection, a repair is performed by: fusing the portion having a risk of breakage and welding a new heat transfer tube to that portion; repairing the portion having a risk of breakage while bypassing a heating medium such as flue gas (refer, for example, Patent Literatures 1 and 2).